It is known in the art that polytetrafluoroethylene can be modified by adding small amounts of comonomers to the polymerization mixture so that the comonomers in polymerized form become part of the resulting copolymer. Two comonomers commonly employed by the art for this purpose are hexafluoropropylene, CF.sub.3 --CF.dbd.CF.sub.2, and perfluoro(propyl vinyl ether), CF.sub.3 CF.sub.2 CF.sub.2 --O--CF.dbd.CF.sub.2. However, these comonomers, because of the presence of fluorine atoms on the double bond carbons, do not have as fast a polymerization rate as the tetrafluoroethylene monomer. It would be desirable to find a comonomer that would react more quickly in order to increase polymerization rates and to promote incorporation of such amounts of the comonomer.